Instantaneous hot water heater and hot air supply



United States Patent 122/(AHI) 122/(AH1) m m m m m W W .m lJ m T ,7 a mmmm d5 L m mamwmmw m m m m M m v uma w.

.m AFPA H. UDHU a corporation of Delaware [54] INSTANTANEOUS HOT WATERHEATER AND HOT AIR SUPPLY 5 ABSTRACT: A water heater f0 7 Claims, 4Drawing figs.

r supplying hot water continu- 101; l22/33(AH1) 51Int.Cl.................. [so

water charge is heated by a two-stage surface heater comprising asurface burner stage followed by a jet impingement stage. The apparatusincludes means for producing a supply of 122/33 hot air.

[5 6] References Cited UNITED STATES PATENTS ,775 6/1908 Dupuis etal.

in as 3% ew m n Patented Oct. 27, 1970 O 0 O 0.0 O O O a -a o o o o o o9 P 0 I 4 dVMWMhE v -4 9-\M u i M Z:

M c 23 7 A c, nor 5 &

H s5 1 8| 33 tm VALVE CONTROL MEANS 'FIG. 2

INVENTOK DEAN TMORGAN BYMWAQMIMB\WM I ATTORNEYS Patented Ot. 19 70 aSheet FIG. 4

ATTORNEYS INSTANT ANEOUS HOT WATER HEATER AND HOT AIR SUPPLY Myinvention relates to heat exchangers, and particularly to a novel hotwater heater that may be associated with an auxiliary air heater forsupplying hot air and water at varying demand rates.

Particularly for modern residential and small commercial requirements,it is highly desirable that a hot water supply be highly compact andinexpensive as well as a reliable source of water that does not varywidely in temperature over a reasonably wide range of demand rates froma zero demand rate. The principal objects of my invention are todecrease the size and cost of hot water heaters, while increasing theirefficiency and reducing the dependence ofhot water temperature on demandrate. Another object is to facilitate the provision of a supply of hotair as a byproduct of the water heating process without interfering withthe temperature of the hot water supply.

The above and other objects of my invention are attained by a novelwater heater construction in which a sealed tank of water is used as athermal storage intermediate and serves directly to heat water from thecold water supply through a thin coil of copper tubing disposed in thetank and adapted to be connected to the supply. The tank is preferably athin. flat rectangular metal box, over the wide sides of which aredisposed surface heaters. Outside of the surface heaters is an insulatedhousing defining, with the tank walls, a gas space through which burningfuel can pass to heat the water tank. Preferably, the surface heatersare gas-fired and comprise an inlet stage consisting of a radiatingsurface burner followed by an outlet stage of jet impingement heating. Ablower is disposed to draw gas and air through the heater, and aconventional pilot control is provided for disconnecting the fuel supplyunless the pilot is lit. The temperature of the water in the 'tank isused as a control medium for regulating the flow rate of fuel to theburner. By that arrangement, the charge of water serving as a thermalstorage intermediate can be maintained in a desired temperature rangewhile the heat taken out in the water coil fluctuates with demand. And,when the water temperature is reduced by a large demand, a highertemperature is available almost immediately by simply reducing thedemand.

An accessory to the water heater of my invention is an air heatercomprising a heat exchanger having a vapor connection to the water tankand a condensate return line to the tank. Since the water temperature isused as the control variable, it is inmaterial whether heat is removedfrom the water in the tank by the hot water coil or by the air heater.Because of the heat capacity of the thermal storage intermediate, thedemand rates of either can be varied over a relatively wide rangewithout materially affecting either the hot air supply or thetemperature of the hot water produced.

The water and air heating apparatus of my invention will best beunderstood in the light of the following detailed description, togetherwith the accompanying drawings, of a preferred embodiment thereof.

In the drawings,

FIG. 1 is a front elevational view, with parts shown in cross sectionand parts broken away, of a hot water heater in accordance with myinvention that is adapted to be connected to an auxiliary hot airheater;

FIG. 2 is a side view of the apparatus of FIG. 1, with parts shown incross section and parts broken away;

FIG. 3 is a cross-sectional view in plan of the apparatus of FIG. 1,taken substantially on the lines 3-3 in FIG. 1; and

FIG. 4 is a schematic orthogonal sketch of the apparatus of FIGS. 1through 3 shown associated with an accessory air heater in accordancewith my invention, with parts broken away.

Referring to FIGS. 1 through 4, the novel air and water heater of myinvention comprises a rectangular outer housing 1 of sheet metal or thelike, such as carbon steel of approximately 0.035 inches in thickness.The outer dimensions of this rectangular sheet metal housing may beselected to suit the maximum hot water flow rate and temperature asdesired, but for a unit suitable for supplying from 0 to 3 gallons perminute of '160F. hot water produced by heating 60F. incoming cold water,the overall outside dimensions may be 14 inches by 25 /2 by 4 /8 inchesdeep. Such a size is convenient for installation in space normallywasted in a house, for example, between the studs of a partition.

Within the outer metal housing 1 is a layer of insulation 3 with theillustrative dimensions cited above, the insulation is preferably a 1%inch layer of glass fiber insulating material. As best shown in FIGS. 2and 3, on the wide sides of the insulating housing just described arefire walls 5 and 7 of sheet metal, such as low alloy steel of 0.035inches in thickness.

A thin flat rectangular tank generally indicated at 9 is disposed withinthe insulated housing described above. The tank 9 may be made fromcarbon steel with a wall thickness of about one-sixteenth of an inch,and, in the illustrative example given, may be 13 inches wide by 24inches high and 2% inches deep.

The cold water supply line I1 is connected to the inlet side of a heatexchanger generally designated at 13, that may comprise inch coppertubing 15 formed into a flat open coil and sinously disposed to makeeight passes in the tank 9 as shown. Preferably, the tubing 15 isprovided with vertical fins l7 schematically indicated in FIGS. 1 and 2but shown more clearly in FIG. 3 as preferably comprising 12 fins. Theouter diameter of the finned portion of the tubing may be approximately1% inches.

The output end of the tubing 15 is connected to a hot water supply line19 leading to distributing valves schematically indicated at 21, such asthe sink and tub faucets of a house, which serve to determine the demandrate for hot water at any time. The connections to the heat exchanger 13of course pass through sealed fittings in the tank 9, for example, thelines leading into the tank may be brazed to it.

As indicated in FIGS. 1 through 3, the end walls 23 and'25 of the tank 9are essentially in contact with the insulation 3. The bottom wall 27rests on the insulation 3 at the bottom of the outer housing, and thetop wall 29 is spaced from the insulation 3 at the top of the outerhousing. The wide side walls 31 and 33 of the tank are spaced from thefire walls 7 and '5, respectively, to provide gas passages between eachwall 31 and 33 of the tank and its adjacent fire wall.

As best shown in FIGS. 1 and 2, openings 35 and 37 at the bottom of theouter housing admit air to the entrance end of the gas passages justdescribed. A gas impeller having an inlet housing schematicallyindicated at 39 is connected to a suitable opening in the upper part ofthe housing 1, 3, and an outlet port 41 suitably vented to a flue isarranged to provide a draft of gas upwardly in the passages between thetank 9 and the fire walls 5 and 7. As schematically indicated, the gasimpeller may be provided with a rotor 43 driven by a conventionalelectric motor 45.

Sealed within the tank 9 is a fixed charge of thermal energy storagefluid, preferably a charge 47 sufiicient to cover the heat exchangercoils, but leaving a vapor space 49 at the top of the tank. In practice,it is preferred to use purified water to which a rust inhibitor has beenadded as the thermal storage fluid.

As best shown in FIGS. 1 and 4, heat for an accessory source of hot airmay be supplied by a closed system including a vapor line 51 connectedto the tank and extending through outer insulation 53 to a heatexchanger coil schematically indicated at 55 and located in an air duct57. An air blower generally indicated at 59 may be provided in the duct57 to force cold air over the coils 55 and produce a stream of warm airfor such purposes as hair and hand drying or for space heating.Condensate formed in the heat exchanger 55 is returned to the tank bygravity through a return line 61 provided with outer insulation 63.These fittings can be omitted if a hot air source is not desired.

A two-stage surface heater is mounted in each of the passages formedbetween the fire walls 5 and 7 and the tank 9. Each such heater includesas a first stage adjacent the entrance end of each passage 5 sheet 65 ofporous material. The material 65 may be ametal screen, but is preferablyof relatively thick porous ceramic material such as that described inU.S. Pat. Nos. 3,l79,156 and 3,l9l,659 to Weiss et al. In operation,combustible gas flowing through the sheets 65 is ignited at the innersurface, and, by heating that surface, promotes heat transfei' byradiation as well as by conduction and convection. The incoming gasthrough the relatively thick porous ceramic wall is heated, reducing thetemperature of the outer wall of the material.

The sheets 65 are secured at the .bottom to the lower wall of the outerhousing, and at the top to brackets 67 that are in turn secured to thefire walls 5 and 7. It will be apparent that by this arrangement gasflowing upwardly through the passages around the water tank will enterthrough the openings 35 and 37 on the outsides of the porous ceramicsheets 65 and will pass through the sheets into contact with the wallsof the tank 9. Then, around the baffles 67, gas will be directed to theoutside of the second stage of each heater. This second stage adjacentthe exit end of the passage formed adjacent the wide walls of the tankcomprises a jet impingement heater section, best shown in FIGS. 2 and 3,and formed by two sheets of metal 69 provided with perforations as at71. The sheets 69 are connected at their lower ends to flanges 73secured to the walls 31 and 33 of the water tank. At their upper ends,the plates 69 are secured to flanges 75 formed by bending over the upperedges of the fire walls 5 and 7. The jet impingement heater sectionsfunction in the manner shown and described in US. application forLetters Pat. Ser. No. 446,476, filed on Mar. 29, [965 now US. Pat. No.3,416,01 l issued Dec. 10, 1968 for Heat Exchangers by Felix .l. Lyczko,and assigned to the assignee of my application, and US. application forLetters Pat. Ser. No. 694,744, filed on Dec. 29, 1967, by Pierre J.Brosens and Dov. Z. Glucksman for Radiant and Convective Burner, andassigned to the assignee of our application.

Essentially, the second stage heater plates 69 function to directburning gases entering from the first stage section around the battle 67and outside of the plate 69 into jets of hot gases through the apertures71 impinging on the walls of the tank 9. Basically, the heating jetsformed by the apertures in the plates 69 serve to increase the heattransfer coefficient considerably more than the effective heat transfersurface is reduced by their introduction without materially affectingthe effective temperature drop across the heat transfer surface, thusmaterially improving efficiency.

Fuel, and preferably natural gas, is supplied from a supply line 77,shown in FIGS. 2 and 4, through a conventional set of one or more valvesschematically indicated at 79 and a pair of supply lines 81 and 83 totwo manifolds 85 and 87 located in the entrance ends of the passagesoutside of the surface burner sheets 65. Fuel control may be essentiallyconventional in that it comprises valve control means schematicallyindicated at 89 for controlling the valve set 79, when a pilot 9] is litas sensed by a temperature responsive element, and at a rate needed tomaintain the temperature of the water charge 47 in the tank 9 within apredetermined range of, for example, between 190 and 200F., as sensed bya temperature sensing element 95 mounted in the tank and connected tothe valve control means. Alternatively, if desired, the pressure of thewater in the tank 9 may be used as the control variable.

Preferably, a relief valve 97 schematically indicated at the upper endof the water tank 9 is provided to prevent destructive bursting of thetank in the event of a malfunction involving overheating. The reliefvalve 97 may be connected to a vent line 99 leading outside of thebuilding in which the heating unit is located.

A connecting slot 101 is formed in the insulation adjacent the side wall23 of the tank 9 to form a gas passage by means of which gas admittedfrom the manifold 87 will be ignited when the pilot 91 is lit and gasadmitted from the manifold is ignited by the pilot. The slot 101 forms achannel through which the pressure drop experienced when the gas fromthe manifold 85 is ignited propogates flame around through the slot 101to the gas-air mixture on the other side of the tank.

In operation, when the valve set 79 is opened to admit gas to themanifolds 85 and 87 and the pilot is lit, a mixture of air and gas drawninto the passages between the tank 9 and the walls 5 and 7 will beignited on the sides of the surface heater elements 65 adjacent the tankwall, heating the tank 9 and causing local boiling of the charge 47.Approximately 60 percent of the total fuel thermal rate is transferredto the tank 9 in this first stage, primarily by radiant heat transferbut also with some forced convection. The hot combustion gases leavingthe first stages of the burners heat the tank 9 through the jetimpingement stages 69, in which about 20 to 25 percent of the total fueland thermal energy is transferred from the combustion gases to thecharge 47. The location of the blower 44 downstream of the heaterprovides a pressure below atmosphere in the heater, thus effectivelyprotecting against gas leakage out of the unit when it is in operation.

With the apparatus shown in FIGS. 1 and 4, including the air heater 55,heat may be drawn from the charge 47 in the tank 9 either by the airheater 55, by the heat exchanger 13 to heat the water supplied from theline 1 l, or by both. The rate of heat extracted in this manner willdetermine the demand for fuel made by the charge 47, as determined byits temperature sensed by the responsive element 95, and communicated tothe valve control means 89. It will be apparent that the heat demandsmade by the hot water supply and the air heating supply can thusfluctuate fairly widely without materially effecting the temperature ofthe hot water supply to the line 19. i

For example, the water temperature may drop to approximately l60F. atthe maximum 3 gallons per minute rate, or somewhat lower if the demandrate exceeds 3 gallons per minute, but still sufiiciently high to beuseful, and rise to F. or so at a zero demand rate. Should hotter waterbe desired at any time when demand has lowered the temperature, merelyreducing the demand will quickly supply it. In order to further smooththe operation of the system, a mixing valve may be provided in aconventional manner well understood in the art for mixing the output hotwater in the line 19 with such proportions of cold water as necessary tomaintain a constant temperature regardless of demand rate.

if a low demand, high temperature water source is desired, such as a F.source for coffee making or the like, an extension of the heat exchanger13 may be provided. For example, a tee connected to the line 15, insidethe tank 9 and upstream of the outlet 19, may be connected to an extralength of finned tubing leading to a second outlet line. The additionalheat exchanger thus provided will inherently provide a higher watertemperature at any demand rate.

While I have described my invention with respect to the details of apreferred embodiment thereof, many changes and variations will occur tothose skilled in the art upon reading my description, and such canobviously be made without departing from the scope of my invention.

I claim:

1. A hot water heater, comprising a sealed rectangular metal tank, aheat exchanger mounted in said tank and adapted to be connected to asource of water to be heated, a charge of water sealed in said tankoutside of and covering said heat exchanger, a vapor space in said tankover said charge of water, insulating wall means surrounding said tankand spaced at least from first and second parallel side walls of saidtankto form gas passages along said first and second walls from anentrance end forming an air inlet adjacent one end of said tank to anexit end adjacent the opposite end of said tank,

surface heaters comprising flat gas permeable sheets in said passagesand spaced from and parallel to said first and second walls, and meansfor supplying combustible gas to said entrance end.

2. The apparatus of claim 1, in which each of said heaters comprises asheet of porous ceramic material adjacent the entrance end of eachpassage and a sheet of perforated metal forming a jet impingement heatersection adjacent said porous ceramic sheet and said entrance end.

3. The apparatus of claim 2, further comprising an air heater, means forsupplying vapor from said tank to said heater, and means for returningcondensate from said heater to said tank.

4. The apparatus of claim 2, further comprising means responsive to athermodynamic property of the water in said tank for controlling thesupply of gas to said burners to maintain the value of said propertywithin a predetermined range.

5. The apparatus of claim 1, in which said first and second walls havedimensions large with respect to the distance between them, and in whichsaid heat exchanger comprises a flat open coil of finned metal tubingsinuously disposed in said tank.

6. A hot water heater, comprising an enclosed metal water tank, a heatexchanger in said tank, means for connecting a water supply line to saidheat exchanger, a charge of water in said tank outside of and coveringsaid heat exchanger and less in volume than the volume inside said tankand outside said heat exchanger, an insulated housing surrounding saidtank and forming a bifurcated gas passage with said tank extending froman open entrance end adjacent a first end of said tank along at leastfirst and second opposite sides of said tank to an exit end adjacent asecond end of said tank opposite said first end, a two-stage surfaceheater mounted adjacent said first side, a two-stage surface heatermounted adjacent said second side, each of said two-stage heaterscomprising as the first stage a surface burner including a sheet ofporous material adjacent said entrance end and spaced from and parallelto said side to which it is adjacent, and as the second stage a sheet ofmetal perforated to form a jet impingement heater located between saidporous sheet and said exit end and spaced from and parallel to said sideto which it is adjacent, the sheets comprising each two-staged heaterhaving approximately equal areas which together approximate the area ofthe side to which they are adjacent, means for admitting gas in saidpassage of each surface burner adjacent said entrance end, baffle meansformed between each first and second stage to direct gas from said firststage outside of the sheet forming said second stage, and blower meansconnected to said passage at said exit end to draw air and gas throughsaid passage.

7. In a hot water heater, a heat exchanger, means for supplying water tobe heated to said heat exchanger, first wall means forming a sealedrectangular metal tank containing a charge of heat transfer fluid andenclosing said heat exchanger, said tank having two spaced oppositeparallel walls having dimensions large with respect to the distancebetween them, second wall means forming a gas passage with said firstwall means and a surface burner mounted between said first and secondwall means, said burner comprising a sheet of gas-permeable ceramicmaterial spaced from and parallel to at least one of said parallelwalls.

